1. Field of the Present Invention
The present invention relates to a solar cell, and a method and an apparatus for manufacturing the same.
Furthermore, the present invention particularly relates to a method for manufacturing a solar cell, an apparatus for manufacturing a solar cell, and a solar cell, where it is possible to shorten the length of time for a heat-treating when a diffused layer is formed in a silicon substrate and possible to manufacture a solar cell having the photoelectric conversion efficiency that is equal to that of a conventional solar cell.
This application claims priority from Japanese Patent Application No. 2008-115977 filed on Apr. 25, 2008, the contents of which are incorporated herein by reference in their entirety.
2. Background Art
In recent years, regarding solar cells having a high level of power generation capability by sunlight, various improvements have progressed with demand for clean energy.
As solar cells, conventionally, a solar cell manufactured using a silicon series material is representative, a single-crystalline silicon solar cell employing single-crystalline silicon, a polysilicon solar cell employing polysilicon layer, an amorphous silicon solar cell employing an amorphous silicon layer, and the like are known.
A single-crystalline silicon solar cell has a structure in which, for example, a diffused layer in which phosphorus (P) that is an n-type dopant is diffused in silicon single-crystalline, an anti-reflective film made of silicon nitride (Si3N4) or the like, and a top electrode are formed on a top face of a p-type single-crystalline silicon substrate in this order, in addition, a BSF layer and a bottom electrode are formed on a back face of the silicon substrate in this order.
A texture structure for anti-reflection is formed on the top face of the single-crystalline silicon substrate by texture etching.
In addition, the diffused layer is obtained by heat-diffusing phosphorus (P) in the above-described top face of the silicon substrate; as a method for diffusing phosphorus (P), a gas diffusion method, a method for applying and diffusing, or the like may be used (Japanese Unexamined Patent Application, First Publication No. H06-29562 and Japanese Unexamined Patent Application, First Publication No. 2004-247364).
Since impurities remain on the surface of the diffused layer, the surface of the diffused layer is rinsed with hydrofluoric acid or the like in order to remove the impurities.
Consequently, in a solar cell manufacturing step, a substrate is once removed from an apparatus used for a diffusing step in an air atmosphere, and is rinsed out; furthermore, it is necessary to bring in the rinsed substrate into a vacuum apparatus in which an anti-reflective film is formed.
In addition, as a method for forming a top electrode, a so-called fire-through process is employed (Japanese Unexamined Patent Application, First Publication No. H5-259488, Japanese Unexamined Patent Application, First Publication No. H10-233518, and Japanese Unexamined Patent Application, First Publication No. 2000-323735). In the fire-through process, a silver paste is applied on the anti-reflective film so as to form a predetermined pattern, the silver paste is baked, a silver electrode is thereby formed, and the silver electrode breaks through the anti-reflective film in contact with the diffused layer by the baking.
However, in conventional silicon solar cells, a heat-treating for a long period of time is necessary to heat-diffuse phosphorus (P) on the top face of the silicon substrate, two times or more of heat-treating is necessary in addition to forming the top electrode; as a result, there are problems in that the manufacturing time, the number of steps, and the cost of manufacturing increase.
In addition, it is necessary to rinse the substrate after diffusing, the manufacturing time and the number of steps increase, and there is thereby a problem in that the throughput of manufacturing solar cells is degraded.